Conventionally, an on-vehicle radar apparatus is known. The on-vehicle radar apparatus emits radar waves (millimeter waves and other waves) as transmission waves across a predetermined angle around a vehicle for fixed periods of time, receives their reflected waves, and then detects objects around the vehicle.
In this type of radar apparatuses, methods, such as monopulse, phased array, multiple signal classification (MUSIC), and digital beam forming (DBF) are known, as an azimuth detection method for detecting the azimuth of a target which has reflected radio waves based on phase differences between signals received using a plurality of antenna elements.
These azimuth detection methods calculate an azimuth α of a target which has reflected radio waves based on a phase difference Δθ [rad] generated between reception signals that are received on channels, because a path difference ΔL of radio waves traveling between the target and the antenna elements is different depending on the combinations of the antenna elements (in the following, also referred to as “channels”).
However, as shown in (a) in FIG. 13, in this case, a so-called phase wrapping occurs, which causes no difference in the phase difference between Δθ=θo (|θo|<n) and Δθ=θo±2nn (n=1, 2, . . . ).
On this account, when a target is present in an azimuth angle region (in the following, referred to as “an azimuthal area”) A0 corresponding to a range in which the phase difference Δθ is in a range of −n to +n [rad], the azimuth of the target can be correctly detected. However, when a target is present outside the azimuthal area A0, i.e., when a target is present in an azimuthal area Am corresponding to a range in which the phase difference Δθ is in a range of (2m−1)n to (2m +1)n [rad] (m is an integer not equal to zero), the azimuth of the target is falsely detected that the target is present in the azimuthal area A0 (see (b) in FIG. 13).
In other words, a so-called grating ghost is falsely detected as an actual target.